Charge transport and rectification in molecular junctions formed with carbon-based electrodes

Taekyeong Kim, Zhen Fei Liu, Chul-Ho Lee, Jeffrey B. Neaton, Latha Venkataraman

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

Molecular junctions formed using the scanning-tunneling-microscope-based break-junction technique (STM-BJ) have provided unique insight into charge transport at the nanoscale. In most prior work, the same metal, typically Au, Pt, or Ag, is used for both tip and substrate. For such noble metal electrodes, the density of electronic states is approximately constant within a narrow energy window relevant to charge transport. Here, we form molecular junctions using the STM-BJ technique, with an Au metal tip and a microfabricated graphite substrate, and measure the conductance of a series of graphite/amine-terminated oligophenyl/Au molecular junctions. The remarkable mechanical strength of graphite and the single-crystal properties of our substrates allow measurements over few thousand junctions without any change in the surface properties. We show that conductance decays exponentially with molecular backbone length with a decay constant that is essentially the same as that for measurements with two Au electrodes. More importantly, despite the inherent symmetry of the oligophenylamines, we observe rectification in these junctions. State-of-art ab initio conductance calculations are in good agreement with experiment, and explain the rectification. We show that the highly energy-dependent graphite density of states contributes variations in transmission that, when coupled with an asymmetric voltage drop across the junction, leads to the observed rectification. Together, our measurements and calculations show how functionality may emerge from hybrid molecular-scale devices purposefully designed with different electrodes beyond the so-called "wide band limit," opening up the possibility of assembling molecular junctions with dissimilar electrodes using layered 2D materials.

Original languageEnglish
Pages (from-to)10928-10932
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume111
Issue number30
DOIs
Publication statusPublished - 2014 Jan 1

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Keywords

  • Density functional theory
  • Graphite electrodes
  • Molecular circuits

ASJC Scopus subject areas

  • General

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